Keyframe seconds doesnt fit the animation
Snap keyframes to frames
Imported animation seems to be scaled down in time, three keyframes in frame is not usual. So original was probably designed for higher FPS (frame per second).
First you need to scale keyframes up, but by default blender use Snap to Nearest Frame, that cause in your case deleting (merging) all keyframes in between frames.

To avoid that, change to No Auto-Snap

In Pose mode select all bones. Go to Dope Sheet, select all keyframes and scale S them up with Current frame at zero, in your case scale to 3.482 seems to fit most of the keyframes on frame position. (Hard to say why they are not set precisely.)

Now you can switch Snap to Nearest Frame back and with all selected press G to move, but you dont really want to move, just move a bit so keyframes jump on frame positions and hit enter. Now you should have all keyframes aligned to frames.

Run cycle duration 0.76666s
Your import in length of 19 frames fits approximately to 25 fps. If you want to scale keyframes to fit frames you would have to increase FPS (frame per second).
Scaling keyframes per frame gives 65 frames with first keyframe on frame 1 (that is common start for blender). Last keyframe generates jump in motion, so I delete them. Since you know you have like 64 frames that should takes 0.766666s you should change fps to (64/76.6666%*100%) 84 fps. I dont know if there are some standards for game cycles, but I expected 60 or 120 so it is a bit weird.



Note:
BTW I don't have any shake even with your blend. So if you are OK to keep 24 fps with just 19 frames that with merged all keyframes in between - just select all bones in pose mode and press G to move a bit with mouse over Dope Sheet and release, keyframes jumps to frame position.